With the next-generation of Extremely Large Telescopes (ELTs), the demands of adaptive optics real-time control (AO RTC) increase massively compared to the most complex AO systems in use today. Green Flash, an ongoing EU funded project, is investigating the optimal architecture for ELT scale AO RTC, with an emphasis on GPU and many core CPU solutions. The Intel Xeon Phi range of x86 CPUs is our current focus of investigation into CPU technologies to solve the ELT-scale AO RTC problem. Built using Intels Many Integrated Core (MIC) architecture incorporating 64 general purpose x86 CPU cores into a single CPU package paired with a large pool of on-chip high bandwidth MCDRAM, the Xeon Phi includes many of the advantages of current technologies. The current generation Xeon Phi is readily compatible with standard Linux operating systems and all of the tools and libraries, and as a standard socketed CPU it eliminates the latency introduced by the extra data transfers required for previous Xeon Phis and other accelerator devices. The Durham Adaptive Optics Real-time Controller (DARC) is a freely available, on-sky tested, fully modular, x86 CPU based AO RTC which which is ideally suited to be a basis for our investigation into ELT scale AO RTC performance. We present a proof of concept AO RTC system, in collaboration with the Green Flash project, for ELT scale MCAO, with the requirements of the MAORY AO system in mind, using an optimised DARC on Xeon Phi hardware to achieve the required performance.
The Green Flash initiative responds to a critical challenge in the astronomical community. Scaling up the real-time control solutions of AO instruments in operation to the specifications of the AO modules at the core of the next generation of extremely large telescopes is not a viable option. The main goal of this project is to design and build a prototype for an AO RTC targeting the E-ELT first-light AO instrumentation. We have proposed innovative technical solutions based on emerging technologies in High Performance Computing, assessed this enabling technologies through prototyping and are now assembling a full scale demonstrator to be validated with a simulator and eventually tested on sky. In this paper, we report on downselection process that led us to the final prototype architecture and the performance of our full scale prototype obtained with a real-time simulator.
Adaptive Optics (AO) is a necessary technology for ensuring the success of the next generation of extremely large telescopes (ELTs). It’s used to help mitigate the perturbing effects of Earth’s atmosphere on the incoming light from astronomical objects and will be an integral part of ELTs for obtaining close to diffraction limited images. To maintain a correction of the incoming wavefront under dynamic atmospheric conditions, which can change significantly on the order of milliseconds, the frame-by-frame reconstruction must be operated in real-time, with hard limits on the time interval between measuring the disturbance and applying a correction. The main problem size for AO RTC increases with the 4th power of telescope diameter and so the computational demands of AO RTCs for ELTs, with primary mirror diameters between 20-40m, increase significantly compared to the current generation of 10m class telescopes. This makes the investigation into and the development of real-time controllers (RTCs) for ELT scale AO systems critical for ensuring the effectiveness of these instruments for first light. Green Flash, which is an ongoing EU funded project, has the aim of investigating the optimal hardware architecture for ELT scale AO RTC, with an emphasis on GPU and Xeon Phi solutions. The Intel Xeon Phi, built using Intel’s Many Integrated Core (MIC) architecture, incorporates ≥64 general purpose x86 CPU cores into a single CPU package paired with a large pool of on chip high bandwidth MCDRAM, it has many of the advantages of current technologies without some of the more significant drawbacks. The most computationally intensive aspects of most AO RTC pipelines are large matrix-vector multiplications mainly used to compute the reconstructed wavefronts which are highly parallelizable and are generally memory bandwidth bound. This makes the Xeon Phi with it’s large CPU count and high bandwidth memory ideally suited for acceleration of the reconstruction task and therefore for ELT scale AO RTC. The most recent incarnation of the Xeon Phi platform is available as a standard socketed x86 CPU allowing previous efforts made in developing CPU based RTC software to be used as a basis for a Xeon Phi based RTCs with the added advantage that any optimisations made for the MIC architecture can be carried forward to future x86 CPU based systems. The Durham Adaptive Optics Real-time Controller (DARC) is an example of a freely available, on-sky tested, fully modular, x86 CPU based AO RTC which which is ideally suited to be a basis for our investigation into ELT scale AO RTC performance. We present a proof of concept AO RTC system, in collaboration with the Green Flash project, using an optimised DARC on a multi-node homogeneous Xeon Phi cluster to demonstrate the potential of the MIC platform for AO RTC. We will present our methods of optimisation for the C based DARC for the Xeon Phi, including BIOS, kernel and OS tuning as well as considerations for multi-threading and massively parallel algorithm development.
The continuous strive for increased sensitiv ity and higher resolution of space based telescopes can only be satisfied with larger primary mirrors. There are quite a few challenges in launching large mirrors in space such as surviving the stress created from the launch acceleration, deployment, thermoelastic deformations, the gravity release etc. Major constraint to space based application is weight which drives the development of thin, extremely lightweight mirrors. Such mirrors are prone for stress based deformations and need active optics correction chain (AOCC) in order to be operated at their full potential. An AOCC for large monolithic mirrors consists of three key active optics components: corrective element (e.g. deformable mirror or DM), wavefront sensor (WFS) and correction algorithm. In order to assess the feasibility of such a system we have developed an AOCC test stand in a collaboration with the European Space Agency (ESA) a nd Netherlands Organisation for Applied Scientific Research (TNO). With this development we aim to measure the performance and the long-term reliability of an AOCC in controlled laboratory conditions. Our design consists of two separate parts, one where the expected aberrations are generated and another where they are measured and corrected. Two deformable mirrors of 37.5 mm and 116 mm are used, the smallest mirror to generate aberrations and the largest to correct them. For wavefront sensing we are using two different wavefront sensors, an 11x11 Shack-Hartmann as well as phase diversity based at the science sensor. We are able to emulate the conditions for both, astronomy related, and Earth observations. Here, we present the design of the system, including the test stand and the correction algorithms, the performance expected from simulations, and the results from the latest lab tests.
We present the outcomes of an evaluation of middleware technologies for adaptive optics real-time control against the requirements of the Green Flash project, which are derived from the most demanding requirements of proposed first generation E-ELT instruments. The technology down-selection process applied in Green Flash is described, and measured performance of the selected middlewares on the hardware of a Green Flash prototype RTC are presented.